TALLAHASSEE — On a shoestring budget, Andrew Gillum pulled off one of the biggest upsets in Florida political history by racking up startling numbers in the four most populous counties with the highest percentage of black voters.

That strategy was ingrained in the primary campaign for Gillum, the Tallahassee mayor and now the state’s first major party black gubernatorial nominee. While fiercely pushing a progressive message that turned out base voters, Gillum had to overcome a crowded primary field that included more-established and better-funded white candidates, a dynamic not lost on the campaign or outside observers.

Gillum won huge margins over the onetime front-runner, former U.S. Rep. Gwen Graham, in Duval, Orange, Broward and Miami-Dade counties — the metro counties with the state's largest percentage of black voters, according to a USA TODAY NETWORK – Florida analysis of Tuesday’s election results.

Gwen Graham answers a question posed by Chris Cifatte at the Democratic gubernatorial primary debate, held at Florida Gulf Coast UniversityÕs Cohen Center in Fort Myers, Florida on Wednesday, July 18, 2018. Moderated by WINK News anchorÕs Chris Cifatte and Lois Thome, this is theÊfirst time the Florida Democratic Party has hosted a debate of this size for statewide candidates in Southwest Florida. This debate also marks the first time that all five Democratic gubernatorial candidates are together on stage in a formal setting. (Photo: Moriah Ratner/Naples Daily News)

In those four counties alone, Gillum beat second-place Graham by more than 100,000 votes, the analysis shows. Statewide, Gillum beat Graham by more than 46,000 votes in the five-person primary.

“Democrats can’t win in Florida without black voters, and we ran unapologetically on kitchen table issues that make a difference in people’s life,” said Geoff Burgan, Gillum’s campaign spokesman.

Matthew Isbell, a consultant for Graham, said the surprise win by Gillum came down to those counties with the high minority makeup. Graham did better than Gillum in most counties, but many wins were in low-population areas and netted fewer votes.

To win that big in those counties, and make Florida political history, Gillum held about a dozen campaign events in each in the final days of the primary race, Burgan said. That includes attending a “Souls to the Polls” event organized by Broward political leaders and zigzagging around Broward and Miami-Dade counties as part of a seven-day bus tour around the state.

Kevin Cate, Gillum’s political consultant, said for the general election, their strategy will be to convince “all voters,” not just minorities, that Gillum is the best choice for Florida.

Florida Senate Minority Leader Oscar Braynon of Miami Gardens sees a higher turnout for black voters as a key component needed to win the general election against Republican Ron DeSantis, the congressman backed by President Donald Trump who handily won his primary Tuesday.

“It’s a component that has been missing from Democratic campaigns in the midterm in the past years," Braynon said. "Specifically in statewide elections, we end up losing by little margins and they, by that I mean black voters, have not been targeted as much by the Democratic Party.”

In Miami-Dade County, one of his supporters said the energy at his events was obvious.

“I don’t know how to explain it," said Juan Cuba, the Miami-Dade Democratic party chair. "It was electric. It was amazing.”

Gillum’s performance surpassed expectations in Miami-Dade, where former Miami Beach Mayor Philip Levine or Graham were expected to win after earlier polls suggested the two were battling out the front-runner status in the race.

Instead, Gillum beat Graham by a margin of 33,000 votes and Levine by 9,000 votes.

The difference came in how Gillum rallied voters, Cuba said.

“Sometimes the events front-runners hold are just glad-handing,” Cuba said. “With Gillum, it was grassroots energy and it was palpable. He brought a really great message and it felt authentic by basing his message on his own experiences.”

Graphic by Janie Haseman/Naples Daily News

Lifted by an August endorsement of U.S. Sen. Bernie Sanders of Vermont, Gillum gained momentum in the crowded primary where most polls suggested he was trailing in third. He pushed issues such as raising the minimum wage to $15 an hour, Medicare for all, paying Florida teachers a minimum starting salary of $50,000 and investing in vocation training.

In the final days of the primary, his campaign saw the late surge in support and pushed the idea that the message being delivered by the only nonmillionaire candidate was resonating with Florida Democrats.

“The truth is, money doesn’t vote, people do,” Gillum said. “We said that all along the campaign trail and nobody believed us."

Gillum spent a total of $4 million in Florida throughout the campaign, compared to the more than $90 million spent by his opponents. He also did not raise much money. Part of the $6 million he was able to raise relied on financing from Tom Steyer, George Soros and Collective PAC, a group dedicated to electing African-Americans.

Gillum was the only Democrat in the race to call for Trump’s impeachment and joined calls to “abolish ICE,” the U.S. Immigration and Customs Enforcement.

Trump said in a tweet Wednesday that Gillum was DeSantis' “biggest dream” for an opponent, calling him a “failed Socialist Mayor.”